If you mean through your server then you should not use port 25, the corect submission port which is 587 and that will require authentication by the client, you certainly do want to allow anyone to relay through your server without authentication - think of 'spammer'.

If you mean through your server then you should not use port 25, the corect submission port which is 587 and that will require authentication by the client, you certainly do want to allow anyone to relay through your server without authentication - think of 'spammer'.

and it is successful. It successfully sends the mail to the recipient email with no authentication. I have not also added their IP in my MTA trusted networks. Now my concern is, if my zimbra mail server is open to relay, then this is a big problem.